In the manufacture of printable sheets such as business forms, there are many circumstances in which it is desirable to print duplicate information on multiple sheets. This includes printing duplicate information on adhesive labels.
Carbonless-paper forms which transfer images from a top sheet to a base sheet by impact methods or thermal printing methods are well known. Chemical carbonless paper functions by bringing together colorless components that react to produce a legible image. In most carbonless papers, the chemical reaction is similar to that of litmus paper changing color when placed in contact with an acid or alkaline solution. Proper functioning of the chemical carbonless paper is dependent on some means of preventing the colorless components from meeting and reacting until this color-producing reaction is desired. A common method of accomplishing this is through the encapsulation of one of the two components of the image-producing chemical system.
Generally, chemical carbonless papers are prepared in three configurations. One is the coated back (CB) configuration, wherein a sheet of paper has a coating of capsules containing color formers and oil solution, binders and other materials on the back of the sheet. A second configuration is coated front (CF), wherein a sheet of paper has a coating of color developing materials on the front of the sheet. A third configuration is front and back (CFB) which comprises a sheet of paper with a coating of color developers on its front surface and color-forming capsules on its back surface.
When using carbonless paper for impact printers, the pressure applied to the top sheet upon impact of the printhead transfers to the base sheet and any intermediate plies. The localized increase in pressure results in the rupture of the capsules which contain reactive compounds within these sheets. Migration of these compounds, either from sheet to sheet or within the same sheet, results in a reaction of these compounds and the generation of color within a pattern of the original image. Examples of such carbonless forms are described in U.S. Pat. No. 4,938,505, issued to Gruttemeyer et al; U.S. Pat. No. 4,046,404, issued to Treier; U.S. Pat. No. 5,279,875, issued to Juszak et al. and U.S. Pat. No. 5,334,571, issued to Baxter.
The carbonless-paper forms used in direct thermal printers or thermal transfer printers typically comprise multiple layers which contain a thermosensitive coating. These coatings contain thermally activated, color forming compounds which change color by the application of heat from a thermal printhead. The resistors within a thermal printhead rapidly heat the surface to temperatures typically in excess of 140.degree. F. Examples of multilayer recording media with thermosensitive, color forming coatings are described in U.S. Pat. No. 4,853,256, issued to Obringer et al and U.S. Pat. No. 5,686,159 issued to Langan.
With the ability to generate duplicate images with multilayer printable sheets, the space available for other information is increased. For example, the printable sheets with multiple integrated removable labels described in U.S. Pat. No. 5,686,159 need not provide space for each label to reproduce the printing on each label since duplicates of the printed image are formed on underlying labels. It is desirable to extend this capability to heat fused toner-based printing methods.
Carbonless papers which can be used in non-impact laser printing and electrostatographic copiers are disclosed in U.S. Pat. Nos. 5,334,571 and 4,046,404, respectively. However, the images formed with these printers are not duplicated. Separate sheets are printed within these printers and then assembled to form a multi-part form. The duplication process achieved with these carbonless papers is accomplished after the forms are assembled.
It is desirable to provide a multilayer printable sheet which will form duplicate images within a heat fusing toner printer such as a laser printer.